Edexcel GCSE Biology (1BI0) — Cells and Control
Every time you scrape your knee, your body performs microscopic divisions to heal the wound. This process of creating new cells is called mitosis. It is a specific type of nuclear division that produces two completely genetically identical cells, known as daughter cells, from a single parent cell.
These new cells are diploid, meaning they contain two full sets of chromosomes. In humans, a diploid cell contains 46 chromosomes (23 pairs).
To create identical copies, cells must progress through the cell cycle. The actual splitting of the nucleus is just one part of this sequence, which follows a strict order:
Mitosis is essential for three main biological processes:
Biologists often need to calculate how fast cells are dividing or how many cells are present after a certain time.
A single yeast cell divides by mitosis 6 times. Calculate the final number of cells produced.
Step 1: Identify the number of divisions ().
Step 2: Apply the formula for cell division.
Step 3: Calculate the final value.
A student observes a plant root tip under a microscope. They count 120 cells in total, and notice that 18 of them are in the stages of mitosis. Calculate the mitotic index.
Step 1: Identify the values for the formula.
Step 2: Substitute into the Mitotic Index formula.
Step 3: Calculate the final percentage.
If the genes controlling the cell cycle mutate, cells may begin to divide rapidly and uncontrollably. This uncontrolled mitosis leads to the formation of a mass of abnormal cells called a tumour, which can result in cancer.
Students often confuse the 'cell cycle' with 'mitosis'. Remember that mitosis is specifically the division of the nucleus, whereas the cell cycle includes interphase (DNA replication) and cytokinesis too.
In Edexcel mark schemes, you must use the precise terms 'genetically identical' and 'diploid' when describing the products of mitosis; vague phrases like 'the exact same' will not earn the mark.
When outlining the stages of mitosis, ensure you use the term 'equator' to describe where chromosomes line up during metaphase, and 'spindle fibres' for the structures pulling them apart.
Remember that DNA replication happens before mitosis actually begins (during interphase), not while the cell is splitting.
Mitosis
A type of nuclear division that gives rise to two genetically identical diploid daughter cells.
Diploid
A cell or nucleus containing two complete sets of chromosomes, one from each parent.
Daughter cells
The new, identical cells produced at the end of cell division.
Genetically identical
Cells or organisms that contain exactly the same DNA and genetic information.
Cell cycle
The sequence of growth and division that a cell goes through, including interphase, mitosis, and cytokinesis.
DNA replication
The process where a cell makes an exact copy of its DNA before cell division.
Chromatid
One of the two identical halves of a chromosome that has been replicated in preparation for cell division.
Spindle fibres
Protein structures that attach to chromosomes and pull them to opposite poles of the cell during anaphase.
Cytokinesis
The final stage of the cell cycle where the cytoplasm and cell membrane divide to form two separate cells.
Meristems
Regions of unspecialised cells in plants (usually at root and shoot tips) that are capable of dividing by mitosis.
Asexual reproduction
A process resulting in the production of genetically identical offspring from a single parent, without the fusion of gametes.
Clones
Organisms or cells that are genetically identical to their parent and each other.
Interphase
The phase of the cell cycle where the cell grows and DNA is replicated before division begins.
Mitotic Index
A measure of the proportion of cells in a tissue sample that are actively undergoing mitosis.
Put your knowledge into practice — try past paper questions for Biology
Mitosis
A type of nuclear division that gives rise to two genetically identical diploid daughter cells.
Diploid
A cell or nucleus containing two complete sets of chromosomes, one from each parent.
Daughter cells
The new, identical cells produced at the end of cell division.
Genetically identical
Cells or organisms that contain exactly the same DNA and genetic information.
Cell cycle
The sequence of growth and division that a cell goes through, including interphase, mitosis, and cytokinesis.
DNA replication
The process where a cell makes an exact copy of its DNA before cell division.
Chromatid
One of the two identical halves of a chromosome that has been replicated in preparation for cell division.
Spindle fibres
Protein structures that attach to chromosomes and pull them to opposite poles of the cell during anaphase.
Cytokinesis
The final stage of the cell cycle where the cytoplasm and cell membrane divide to form two separate cells.
Meristems
Regions of unspecialised cells in plants (usually at root and shoot tips) that are capable of dividing by mitosis.
Asexual reproduction
A process resulting in the production of genetically identical offspring from a single parent, without the fusion of gametes.
Clones
Organisms or cells that are genetically identical to their parent and each other.
Interphase
The phase of the cell cycle where the cell grows and DNA is replicated before division begins.
Mitotic Index
A measure of the proportion of cells in a tissue sample that are actively undergoing mitosis.
